Comments of the Week #174: from growing black holes to nuclear bombs

There is no special filter necessary to bring out the pink coronal loops near the very edge of the Sun. Image credit: Brett Boller.

“It will shine still brighter when night is about you. May it be a light to you in dark places, when all other lights go out.” ―Galadriel, LOTR, J.R.R. Tolkien

Well, we’ve been anticipating it for months (or years), but this is our very first time meeting up since the total solar eclipse here at Starts With A Bang! Did you get to see it? Was it as spectacular for you as it was for me? I’m already looking forward to 2024, but you can look forward to a podcast coming this next week from me on just how spectacular it was! (With a judicious dose of physics and astrophysics, of course.) Patreon supporters, of course, can get it right now; no waiting! With that said, let’s move on to the scientific stories we covered this past week:

32 images of the 2016 eclipse were combined in order to produce this composite, showcasing not only the corona and the plasma loops above the photosphere with stars in the background, but also with the Moon’s surface illuminated by Earthshine. Image credit: Don Sabers, Ron Royer, Miloslav Druckmuller.

I agree with Ragtag here. I bought a couple of sheets of these and they’re wonderful. They look, to be honest, like Miloslav Druckmuller’s photos (above), and I’ve already sent a few off to some lucky folks. Now that I’ve seen one for the first time, I’m a true believer in their magnificence, and I can’t wait for the next one!

The Newtonian and Einsteinian predictions for gravitational deflection of a distant radio source during the Earth’s orbital period (1 year) due to the Sun. The black dots are 2015 data. Image credit: The deflection of light induced by the Sun’s gravitational field and measured with geodetic VLBI; O. Titov, A. Girdiuk (2015).

From Anonymous Coward on confirming relativity without waiting for an eclipse: “Thanks Ethan, for the indirect link. That picture and its caption was a big enough clue for me to find the paper by Titov and Girdiuk: “The deflection of light induced by the Sun’s gravitational field and measured with geodetic VLBI.” I’d heard about the radio measurements of light deflection from the sun but didn’t know of any primary sources.”

It is incredible how much amazing, quality science has gone on with regards to confirming relativity. In addition to light-bending by the Sun, we do have confirmation of gravitational redshift, the Shapiro time delay, the precession of not just Mercury’s orbit but also Venus’, Earth’s, and Mars’ orbits, the Lens-Thirring effect, geodetic precession, strong and weak gravitational lensing, the Sachs-Wolfe and Integrated Sachs-Wolfe effect, and many others, not the least of which is the direct detection of gravitational waves by LIGO. General relativity is extraordinarily well-confirmed by a whole slew of independent lines of evidence — Govert’s book Ripples In Spacetime that I reviewed just recently — does a wonderful job recounting many of the confirmations. The radio VLBI observations are a good, recent one that I’m happy I can point you towards. Interestingly, many people have worked to take observations, independently, good enough to confirm the original Eddington experiment this past Monday. I’ll let you know if I come across any robust results.

Image credit: photograph by Frank Tuttle of King Triton and Ursula the sea witch from the Little Mermaid at MidSouthCon 34.

From Steve Blackband on who am I: “BTW is the guy in the grey beard and crown you?”

Updated annually since 2009 with each new Halloween photo. If you missed any, they’ve been:

2016: King Triton,

2015: Axe Cop,

2014: Man-o-taur,

2013: Rainbow Dash,

2012: Zangief,

2011: Wolverine,

2010: Macho Man Randy Savage,

2009: Pharaoh Ramses.

Keep speculating as to what 2017 might hold!

As a black hole shrinks in mass and radius, the Hawking radiation emanating from it becomes greater and greater in temperature and power. Once the decay rate exceeds the growth rate, Hawking radiation only increases in temperature and power. Image credit: NASA.

From Omega Centauri on what Hawking radiation is made of: “Since we have a primordial neutrino background at IIRC 1.75K, do black holes also emit Hawking like neutrino radiation? Or does finite rest mass largely suppress this?”

We normally think of Hawking radiation as being radiation (photons) only, and to a first approximation, that’s very likely correct. Why? Because we don’t have enough power in the radiation to — as you intuit — create any particles with non-zero rest mass. Even the rest mass of a neutrino, at the low end at around 10^-6 eV/c^2, is far too great to be created by any black holes that exist today. (The CNB is around 1.95 K, FYI, but falling into gravitational wells leads to greater velocity than that temperature would imply.)

Give it enough time, though; when the mass of a black holes shrinks to a small enough value so that the temperature of Hawking radiation is above the neutrino rest mass energy, or above a few tens of Kelvin, and you’ll start making neutrinos, then electron/positron pairs, and then the really heavy stuff in the last few seconds. What’s interesting is that we’re still not sure what sort of gravitational waves come out at the event horizon, as we don’t have the quantum theory of gravity necessary to go there. Too bad, because gravitons are massless, too!

The 30-ish solar mass binary black holes first observed by LIGO are likely from the merger of direct collapse black holes. But a new publication challenges the analysis of the LIGO collaboration, and the very existence of these mergers. Image credit: LIGO, NSF, A. Simonnet (SSU).

From Michael Mooney on an intended insult that’s actually a compliment: “Ethan consistently makes statements as established facts even though they are theoretical, without empirical evidence and surrounded by debate in the world of physics.”

Yes, you’re very welcome. What you are talking about is called “theoretical physics,” in the sense that we have theories which accurately describe the Universe, which in turn we can use to make predictions about new phenomena that haven’t yet been observed. It is the best, most straightforward use of theoretical physics, and also my favorite: it’s what I built the start of my career on. It’s why we were able to predict gravitational waves, including their properties and waveforms, before we had ever detected them. It’s why a whole slew of science is able to be done at all.

Someday, like many others before you, you may come to appreciate it.

Hawking radiation is what inevitably results from the predictions of quantum physics in the curved spacetime surrounding a black hole’s event horizon. Image credit: E. Siegel.

From klac on what a black hole’s event horizon looks like: “Is the “surface” of the event horizon smooth or roiling? If the latter, does this affect the evaporation rate?”

Smooth, down to the quantum gravity scale. At the scale at which it is imperfect, there will be imperfections in the spectrum of Hawking radiation. If Hawking radiation is ever detectable, the fluctuations will be another 30-something orders of magnitude below that in scale. Good luck.

This Wolf–Rayet star is known as WR 31a, located about 30 000 light-years away in the constellation of Carina. The outer nebula is expelled hydrogen and helium, while the central star burns at over 100,000 K. Image credit: ESA/Hubble & NASA; Acknowledgement: Judy Schmidt.

From John on Wolf-Rayet stars: “These Wolf-Rayet stars would make for a pretty inhospitable Solar System!”

Oh, yes! That is an extremely good point; here are just a few reasons why:

They only live for maybe a few million years before they end their lives,

They change in luminosity by a factor of many over that time,

They blow off many solar masses worth of plasma across any planets present,

They are unstable, flaring stars,

And their spectra are such that they ought to strip the atmospheres off of any potentially habitable world that ever existed around them.

I would say that makes for “pretty inhospitable” indeed.

Sunbeams shining through the trees at Oxford, by Wikimedia Commons user Remi Mathis, under a c.c.a.-by-s.a.-3.0 license.

From CFT on the solar eclipse: “I can get the effect of a complete solar eclipse every time I walk under a leafy tree or enter my house. I call it ‘shade’.”

Walking under a shady tree is to a total solar eclipse what fanning yourself with a folded sheet of paper is to skydiving for the first time. Never seen a total solar eclipse? I highly recommend it; it just might change your outlook on life a little bit.

A shot of the Sun’s corona at the moment of totality, during the Great American Eclipse of August 21, 2017, at Casper Collage Wyoming. Image credit: Gene Blevins/AFP/Getty Images.

From Sinisa Lazarek on eclipse surprises: “Reading your article it’s clear that you had a blast and that you’re still under emotional experience of it. 🙂 I’m glad and happy that you had good weather and that it was great.
But can’t really understand why points 1, 2, 6 and 9 are surprising, especially for scientists.”

Well, the first one (that it didn’t get dark all at once) surprised me, because the Sun is really, really bright, and a penumbral shadow is kind of (no offense to the inanimate objects in the Solar System) garbage compared to the umbral shadow when it falls on the Moon. When total eclipses happen under cloudy conditions — which is how the people I know experienced the 1979 eclipse — it does get dark all at once. So that’s why #1 surprised me.

The second one, as to the size and brightness of the corona, I had only seen photos. Sure, some photos are long-exposure to bring out the detail in the outer corona, but I had expected to see a much smaller corona, akin to what the photo at the very top of the page showed, than what was actually visible to my eye. There’s no way to really know these things for sure, that cannot be preserved on film, until you’ve experienced it for yourself. Being a scientist has very little to do with the human experience you feel with your own body. In more than a theoretical sense alone, we all need to live.

The eclipsed Sun, the visible corona, and the surrounding sky, as blown-up by me multiple times over the original image referenced. Image credit: Joe Sexton / Jesse Angle.

From Pawel on why the Moon’s shadow is so black: “But the question is – why the Moon seems so black during totality? The rest of the sky, beyond the Sun’s corona, is bright because of the light refracted in the atmosphere. Since the Moon is far beyond the atmosphere, shouldn’t it be washed away by the refracted light and appear the same color as the rest of the sky?”

Optics never fails to disappoint with how interesting it is. Here’s a fun thing for you to do: draw yourself a to-scale diagram (it’s tough!) of the Sun, the Moon, and the Earth. Now, extend the Sun’s radius by, oh, let’s say about 40%, just for giggles. Draw those same lines you’d draw for the Corona’s shadow — both umbral and penumbral — that you’d draw for the Sun’s shadow.

If you do, you’ll see how much less coronal light gets through at the Moon’s center than at the surrounding environs. That’s the biggest reason why the Moon’s disk appears dark in comparison to the region outside the Moon’s disk, even when you’re away from the visible corona itself.

A simulated picture of the sky as it might have appeared during the total solar eclipse of August 21st. Regulus (next to the Sun), Mars (top) and Mercury (bottom) may all be visible with clear skies and favorable conditions. Image credit: E. Siegel / Stellarium.

From Steve Blackband on whether he saw Mars or not: “BTW I was starring hard, but I was pretty sure I saw Mars, close to and to the left of the sun, at about 11 o-clock. Am I deluded?”

No, but if it was to the left (east?) of the Sun, it was probably Mercury. If it was to the right (west) of the Sun, it could have been Mars. If it was either of those, they should have been about 12 degrees (throw heavy metal horns with your index and pinkie fingers, held at arm’s length) off from the Sun. If it was much more than that, it was probably Jupiter (to the left) or Venus (bright, to the right), while if it was only about 1 degree off from the Sun, that was probably Regulus.

An illustration of the Sun-Moon-Earth configuration setting up a total solar eclipse. The Earth’s non-flatness means that the Moon’s shadow gets elongated when it’s close to the edge of the Earth. Image credit: Starry Night education software.

From PJ on eclipse mania: “Welcome to the club, Ethan. You seem to show the signs. More, more! Next eclipse, please! At least the next one will see you better prepared now you have first hand experience of the event.”

2024, totality in the USA, and it should be more than twice as long as what I got to see. (Waco, TX, gets 4:15 of totality, while in Mexico they get to over 4:30.) If I get really ambitious, there’s always the 2027 eclipse, just shy of my 50th birthday, which will go over the Iberian Peninsula and then peak near Luxor, Egypt. Maximum totality there is over 6 minutes, and should be among the most spectacularly dark eclipses of the 21st century.

Yes, PJ, I’ve had my first taste and now… well, you know how I teach electric potential energy in college? Bringing in electric charges is like the crack dealer: the first one’s free, but the second one costs you, and then subsequent ones cost more and more… and you’ll pay it if you want it bad enough!

Well, here’s the thing: the above signal that you see works for all objects as long as they’re spherical and not in physical contact with one another. But white dwarfs, about the size of Earth, touch each other (or whatever they’re orbiting) way before something like LIGO would be sensitive to them. LIGO will not see white dwarfs.

On the other hand, BH-BH mergers, BH-NS mergers, and NS-NS mergers have all been very thoroughly modeled. NS-NS mergers, in particular, are expected to produce gamma-ray bursts and leave the signatures I described to you in the article from this week. Are they correct, these predicted signatures? I have a feeling there will be a lot more to come on this topic as the coming weeks unfold…

The brightness/distance relation for light, which is not the same as for gravitational waves. Image credit: E. Siegel.

From Klavs Hansen on the unbearable lack-of-lossiness in gravitational wave astronomy: “A factor ten reduction in energy means that the event needs to be a factor ten closer to be detected?”

Yup. And it isn’t obvious. Light, an electromagnetic effect, is a form of dipole radiation. If you go twice as far away, the brightness dims to one-fourth the original; if you’re ten times as far away, the brightness is 1/100th. But gravitational radiation is quadrupolar radiation, not dipole radiation. It doesn’t fall off as 1/r^2, but rather as 1/r. If you’re ten times as far away, the magnitude is only 1/10th as great. This is good, because that radiation is so weak! It also means, if you wanted to visually detect what was going on with the original merging black holes that LIGO found, they’d need to have merged from within our Solar System, instead of over a billion light years away. There is no good non-technical explanation of this effect that I’ve yet figured out that’s actually still correct.

Our fear of aliens, and their potential hostility towards humanity, has driven much of our public sentiment and presentation of extraterrestrial life. Image credit: plaits / flickr​.

From eric on disagreeing about alien intents: “Consider the species on Earth with reasonably sized brains. most of them can communicate (albeit not like we do). All of them are more closely related to humans in brain structure, instinct, and emotional desires than any alien we will ever meet – hands down, no contest. And yet practically none of them show any interest in wanting to communicate with humans.”

Huh. I suppose we’ve met different intelligent animals. Dogs, cats, dolphins, monkeys, Orang Utans… I’ve met lots of animals that not only want to communicate with humans in general (and me in particular), but that want us to play with them. Play is one of the highest forms of communication, IMO, so… my experience doesn’t mirror yours, I suppose.

The cloud from the atomic bomb over Nagasaki from Koyagi-jima in 1945 was one of the first nuclear detonations to take place on this world. After decades of peace, North Korea is detonating bombs again. Credit: Hiromichi Matsuda.

And finally, from Elle H.C. on the nuclear frontier and mass-energy conversion: “Is nuclear energy the last barrier where mass can be turned into energy, no sub-atomic conversion to worry about, anyone have a crystal ball to foresee ‘the future’?”

Oh no, not at all. You see, even chemical transitions, where electrons hop from one energy level to another, get their energy from mass-energy conversion. It’s just 5-6 orders of magnitude less efficient. But in the other direction, matter-antimatter annihilation (or, in the case of boson-boson interaction, pure annihilation with no distinction between matter and antimatter) is 100% efficient, about 2-3 orders of magnitude better than nuclear energy. It’s pretty incredible what we’ve achieved, but there are reminders that nature is both more subtle than we give it credit for and also capable of being more spectacular than anything we’ve ever yet made come true.

Have a wonderful week, and we’ll be back here tomorrow with more outstanding science on Starts With A Bang!